For example, as a green phosphor that is excised by vacuum ultraviolet light, Zn2SiO4:Mn is well known. This phosphor is advantageous in a high chromaticity (chromaticity coordinates: x=0.21, y=0.72), and a high luminescent efficiency. However, it has the problem that luminance changes fast with time and the life time is short.
As another green phosphor, BaAl12O19:Mn is known. This phosphor also has high color purity and luminescent efficiency, however, it has the problem of short life time.
As a phosphor that improves both the life time and luminescent efficiency, there is known a phosphor in which a rare earth element and transition metal are added concurrently as a luminescent center to crystals having a magnetoplumbite type structure. Concretely, LaAl11O19:Eu2+, Mn (JJAP, 13 (1974) pp. 950-956: Non-patent document 1), SrAl12O19:La, Eu2+, Mn (Philips Technical Review, 37 (1977) pp. 221-233: Non-patent document 2), SrAl12O19:Mn, Ln (Ln: trivalent rare earth element) (Japanese Unexamined Patent Publication No. 2001-139942: Patent document 1) can be recited. In these phosphors, energy moves from the rare earth element to Mn, and more green luminescence is obtained compared to a phosphor only of Mn.
As an intensifying element for intensifying luminescence from Tb, Ce is often used. As a phosphor containing Ce, CeMgAl11O19:Tb is described in J. L. Sommerdijk AND J. M. P. J. Verstegen: J. Luminescence, 9 (1974) pp 415-419 (Non-patent document 3) or in J. L. Sommerdijk AND A. L. N. Stevels: Philips Technical Review, 37 (1977) pp 221-233 (Non-patent document 4) and the like. This is because energy transits from Ce to Tb at a high efficiency since a luminescent energy level of Ce is almost the same with fd transition energy of Tb. The excited Tb emits visible light based on transition from 5DJ to 7FJ′. A green main peak at a wavelength of about 540 nm resulting from transition from 5D4 to 7F5, a blue sub peak at a wavelength of about 480 nm resulting from transition from 5D4 to 7F6, a yellow sub peak at a wavelength of about 580 nm resulting from transition from 5D4 to 7F4, and a red sub peak at a wavelength of about 600 nm resulting from transition from 5D4 to 7F3 are obtained. A CIE color coordinate of luminescence of this phosphor is about (0.31, 0.61). A y component of this color coordinates represents a green component. In luminescence using Tb like CeMgAl11O19:Tb, however, a y value is lower by 0.1 or more, compared to a color coordinate (0.21, 0.72) of Zn2SiO4:Mn, and a color coordinate (0.15, 0.73) of BaMgAl14O23:Mn. In other words, a color purity of green is significantly low, and is not appropriate for a display device.
A phosphor represented by (Ce1-xTbx)(Mg1-a-bZnaMnb)Al2aO2.5+3a (provided that 0<x≦0.6, 0<a+b<1, 4.5≦z≦15) which is coactivated with Mn and Tb is described in Japanese Unexamined Patent Publication No. HEI 5 (1997)-86366 (Patent document 2). This phosphor has a spectrum in which Mn luminescence is added to luminescent light of Tb. Therefore, the chromaticity is improved compared to the aforementioned phosphor, however, there is still a problem that the luminescence amount by vacuum ultraviolet excitation is inferior by about 20% compared with Zn2SiO4:Mn.
Patent document 1: Japanese Unexamined Patent Publication No. 2001-139942
Patent document 2: Japanese Unexamined Patent Publication No. HEI 5 (1997)-86366
Non-patent document 1: JJAP, 13 (1974) pp. 950-956
Non-patent document 2: Philips Technical Review, 37 (1977) pp. 221-233
Non-patent document 3: J. L. Sommerdijk AND J. M. P. J. Verstegen:J. Luminescence, 9 (1974) pp 415-419
Non-patent document 4: J. L. Sommerdijk AND A. L. N. Stevels: Philips Technical Review, 37 (1977) pp 221-233